Field of the invention
This present invention relates to an optical switch and in particular to an optical switch based on V-beam electrothermal actuators and bi-directional movable latched mechanism.
Optical switches can be applied to telecommunication network for bandwidth provisioning, add/drop multiplexing, network protection and network monitoring, etc. Optical switching technology""s main advantage is to route optical data signals without conversion to electrical signals, resulting in the independence of data rate and data protocol. An optical switch typically has a mirror to be switched into and out of a path of an optical signal beam. Switches can often be categorized into xe2x80x9clatchxe2x80x9d and xe2x80x9cnon-latchxe2x80x9d. In a latched optical switch, the mirror reliably remains in a known position of the on or off state of optical switch, even if the external electrical load is removed or lost. On the other hand, a non-latched switch may revert to an unknown position, or even to a position between the switching states, when the external electrical load is removed or lost. Optical switches are typically defined by the number of input and output ports, referred to as Nxc3x97M. Considerable interest has recently been shown in using the MEMS (microelectromechanical systems) technology to make optical switches. Combining the comb-drive actuator with the silicon-on-insulator (SOI), deep-reactive-ion-etching (DRIE) process, and subsequently wet etching process, the MEMS based optical switch devices have been prepared and characterized by, for example, W. Noell, et al., xe2x80x9cApplications of SOI-Based Optical MEMSxe2x80x9d, IEEE J. on Selected Topics in Quantum Electronics, Vol. 8, No. 1, January/February 2002, pp. 148-154; C. Marxer and N. F. de Rooij, xe2x80x9cMicro-Opto-Mechanical 2xc3x972 Switch for Single-Mode Fibers Based on Plasma-Etched Silicon Mirror and Electrostatic Actuationxe2x80x9d, IEEE J. of Lightwave Technology, vol. 17, No. 1, 1999, pp.2-8; W.-H. Juan and S. W. Pang, xe2x80x9cHigh-Aspect-Ratio Si Vertical Micromirror Arrays for Optical Switchingxe2x80x9d, IEEE J. Microelectromechanical Systems Vol. 7, No. 2, 1998, pp.207-213. Prior arts of U.S. Pat. No. 6,315,462, xe2x80x9cFiber Optic Circuit Switch and A Process for Its Production,xe2x80x9d of O. Anthamatten and C. Marxer; and U.S. Pat. No. 6,229,640,xe2x80x9cMicroelectromechanical Optical Switch and Method of Manufacture Thereof,xe2x80x9d N. Zhang have described the utilization of DRIE and wet etching release process technologies to construct the optical switch devices from SOI wafer, or bonded silicon wafers. Such disclosed optical switches comprise a high-aspect-ratio micro-mirror with vertical sidewall and an electrostatic comb drive actuator for controlling the position of micro-mirror. The common comb drive actuator includes a stationary comb finger electrode, and a movable comb finger electrode connected to the micro-mirror via a suspended spring. Said suspended spring is anchored on to a substrate at one end. Electrostatic force for moving the micromirror can be generated by applying voltage to comb drive actuator. The restoration force generated by the deformed spring will pull the actuated micro-mirror return to the initial position. Regarding the application of optical switch, micro-mirror can be moved from the initial off-state (light transmission state) to the actuated on-state (light reflection state, i.e., switching) via applying voltage to comb drive actuator.
However, a continuously applied electrical load on MEMS actuator is necessary to hold the micro-mirror of optical switch staying at the on-state, because we need the force generated by MEMS actuator to balance the restoring force from spring. Therefore, mechanically-bistable mechanism, i.e., latch mechanism, which provides two relative positions both are mechanically stable, is desirable for optical switch to maintain at on-state without electrical power consumption. Prior art of U.S. Pat. No. 6,303,885, of xe2x80x9cBi-stable Micro Switchxe2x80x9d of B. P. Hichwa, C. Marxer, and M. Gale has disclosed a latched optical switch using buckled-beam with the arch-shaped leaf spring geometry driven by a bi-directional movable electrostatic comb actuator. Additionally, prior art of U.S. Pat. No. 6,549,107, xe2x80x9cLatching Mechanism for MEMS Actuator and Method of Fabricationxe2x80x9d of M. Lim, R. Fan, and L. Que has disclosed another kind of latch mechanism for optical switch has been realized by using gripper to clamp the switch at one position.
It is also important for optical switches to have low insertion loss, low polarization dependent loss, and low back reflection loss in practical applications. Combining the MEMS elements with micro-optics provides optical switch devices a free-space light path design approach. This is a key way to make the light beam coming from input fiber become collimated beam shape thereby to gain in better optical performances. The larger collimated beam size, for example, from several tens to hundreds of micrometers, will make better optical performance, and make the acceptable alignment tolerance higher during the device assembly process. However, it will also lead to a requirement that the corresponding MEMS actuator has to be able to provide enough displacement so as to make the micro-mirror fully reflect the incoming light beam. In the conventional design of electrostatic comb-drive actuator, the maximum static displacement of comb actuator is limited by the side sticking effect of comb fingers. The tiny deviations of comb finger and gap width will cause the unbalanced force of both sides of finger electrode, and such deviation is easily induced by microfabrication process. The unbalanced force of both sides of finger electrode is the major contribution factor to the side sticking effect.
Obviously, the conventional MEMS based optical switches using the electrostatic comb drive actuator and buckle beam formed on SOI substrates have encountered the following issues: 1) The large displacement provided by comb drive for gaining in better optical performance in conjunction with optics will lead to design limit of comb drive actuators and very high driving voltage for such comb drive actuators. 2) The necessary force output provided by comb drive for moving the arch-shaped leaf spring from one stable state to the other stable state will require the adopted MEMS actuator generate the needed force. According to the functional requirements for practical applications of optical switches mentioned above, the desirable device features of optical switches include large displacement regarding mirror, large force output from actuator, and latch mechanism for device itself. The present invention then provides novel designs to make the optical switch with aforementioned device features. We now disclose novel designs of latched optical switch based on using electrothermal V-beam actuators and movement translation mechanisms.
In view of the above mentioned optical switch function requirements, the present invention is then objected to provide optical switches using electrothermal V-beam actuators to generate the necessary force output and displacement, and to provide optical switches using structures, links and movement translation mechanism to perform the bi-directional movement and motion, and to provide optical switches using buckle beam spring as the latch mechanism to let reflective mirror shutter maintain at bi-stable positions without electrical power consumption.
The optical switches of the present invention comprise two sets of movable V-beam actuators, a set of buckle beam springs connected to a suspended movable shutter beam with a reflective mirror shutter, and at least a suspended movable translation link at ends of said suspended movable shutter beam. Both ends of this set of buckle beam springs are anchored to the substrate, while center of buckle beam is connected to said suspended movable shutter beam. Force generated by one of the two sets of electrothermal V-beam actuator upon various values of the applied electrical load is against the restoration force from buckle beam springs. The buckle beam is deflected to a range where the force from bended buckle beam spring is balanced to the force generated by actuated V-beam actuator, when the V-beam actuator is under the electrical load. The V-beam actuator can push or pull the suspended movable translation link to move the shutter beam when the buckled beam spring being deflected into opposite direction with deflection equivalent to 133% initial buckle deflection due to the generated electrothermal force against the existing buckle beam spring force. (The value of 133% could be found in the reference of U.S. patent in application No. xe2x80x9c2003/0029705A1xe2x80x9d) Thereafter, the mirror and shutter beam will move from initial position to another position of the bi-stable state. On the other hand, the mirror and shutter beam will be moved by the suspended movable translation link back to the initial position of the bi-stable state, when another one of the two sets of electrothermal V-beam actuator is actuated to pull or push the suspended movable translation link. Thereby the on-off switching operation with latch function is realized by the present invention.
In preferred embodiments, the movement translation mechanism of said optical switch is a mechanism comprising at least one movement translation link connected to said shutter beam, and structure connected to the V-beam actuator along with the arched direction for pushing and pulling the movement translation link. The V-beam actuators can push and pull the shutter beam with reflective mirror shutter via moveable translation link to perform the on-off switching function for optical switch application.
In other embodiments, the two sets of V-beam actuators of said optical switch have their arched directions in parallel toward opposite directions, and each sets of V-beam actuator comprises at least one V-shaped arch beam with two ends anchored onto a substrate. The V-beam electrothermal actuator is elongated and deflected toward the arched direction of V-beam when electrical load is applied cross the two ends of V-beam. Thereby one directional motion and movement is generated by driving one of the two sets of V-beam actuators. In order to make two-way motion and bi-directional movement, two sets of V-beam actuators of said optical switch are arranged in a way that their actuation and moving directions are parallel and opposite. Thus one set of V-beam actuator is responsible for pushing the moveable translation link, and the other set of V-beam actuator is responsible for pulling the moveable translation link. In conjunction with the movement translation link structure, the on-off switching operation is realized by using bi-directional movement generated by said two sets of V-beam actuators.